Photocatalytic mixture for the degradation of nitrogen oxides

Abstract

A first aspect of the invention consists of a photocatalytic mixture designed to obtain degradation of nitrogen oxides through synergic combination of the two compounds: TiO2, in any of its crystalline phases or in amorphous state, and one or various feldspars such as carnegeit or nepheline.A second aspect of the invention consists of obtaining said combination giving rise to products with the capacity to degrade nitrogen oxides.

Description

OBJECT OF THE INVENTION[0001]A first aspect of the invention refers to a photocatalytic mixture designed to degrade nitrogen oxides through a synergic combination of two compounds: TiO2, in any of its crystalline phases or in amorphous state, and one or various feldspars such as carnegeit or nepheline.[0002]A second aspect of the invention refers to obtaining said combination giving rise to products with the capacity for degrading nitrogen oxides.BACKGROUND TO THE INVENTION[0003]Feldspars are aluminosilicates comprising aluminium, silica and oxygen. Their structure consists of a silica base, part of which has been isomorphically replaced by aluminium. As they become unbalanced the charges are compensated with metal cations (K+, Na+, Ca+2). These solid materials are able to absorb compounds on their surface.[0004]In turn, related materials exist known as feldspartoids which are a group of tectosilicates, similar to feldspartoids but having a different structure and a much lower silic...

AI Technical Summary

Benefits of technology

[0041]Following this first synergic effect associated with an increase in the activity of the photocatalytic mixture during a certain period of time, a second synergic effect is observed. When this initial period of time has passed, which is of the same order of magnitude as the period during which the TiO2 in its pure state is active, it is verified that the photocatalytic mixture does not lose its activity but stabilises round an asyntotically constant value which is maintained for a period which is considerably longer than for a photocatalyser containing pure TiO2.

[0042]Both synergic effects are relevant because the first enhances the degradation capacity of the NOx and the second permits the photocatalytic mixture to operate continuously and in a stationary manner for a considerably longer period than that which operates with pure titanium dioxide.

[0043]In order to highlight the synergic effect of the photocatalytic mixture compared with its components separately, FIG. 3 shows a graph obtained on the basis of data from an experiment consisting of checking the capacity for removing nitrogen oxides through the use of carnegeit with a certain amount of nepheline.

[0044]It has already been described how feldspartoids only have the capacity for removing nitrogen oxide from the air flow based on an effect of superficial adsorption.

Problems solved by technology

These pores are not interconnected and do not permit diffusion of ions or molecules in their interior.

The application of both feldspars and feldspartoid materials to alleviate the problem of atmospheric pollution caused by nitrogen (NOx) thus reducing the concentration of these gases in contaminated air presents the problem that, although the feldspars and feldspartoid materials have some capacity for adsorption, when they are saturated their capacity for reducing the percentage of NOx disappears.

Thus, the maximum amount of NOx adsorbed is greater when the NOx is in a dry air stream than when it is in a damp air stream, as in the latter case adsorption of the NOx competes (unfavourably) with the adsorption of water in the damp air.

The elimination of NOx from the air in this case is certainly carried out through chemical transformation of the nitrogen oxide; however, experiments performed under laboratory conditions show that the activity of the TiO2 is restricted, given that a drop in the titanium oxide activity occurs, until the final ending of said activity.

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